Rotary regenerative heat exchangers are commonly used to recover heat from flue gases exiting a furnace, steam generator or flue gas treatment equipment. Conventional rotary regenerative heat exchangers have a rotor mounted in a housing that defines a flue gas inlet duct and a flue gas outlet duct for the flow of heated flue gases through the heat exchanger. The housing further defines another set of inlet ducts and outlet ducts for the flow of gas streams that receive the recovered heat energy. The rotor has radial partitions or diaphragms defining compartments therebetween for supporting baskets or frames to hold heat transfer sheets.
The heat transfer sheets are stacked in the baskets or frames. Typically, a plurality of sheets are stacked in each basket or frame. The sheets are closely stacked in spaced relationship within the basket or frame to define passageways between the sheets for the flow of gases. Examples of heat transfer element sheets are provided U.S. Pat. Nos. 2,596,642; 2,940,736; 4,363,222; 4,396,058; 4,744,410; 4,553,458; 6,019,160; and 5,836,379.
Hot gas is directed through the heat exchanger to transfer heat to the sheets. As the rotor rotates, the recovery gas stream (air side flow) is directed over the heated sheets, thereby causing the recovery gas to be heated. In many instances, the recovery gas stream consists of combustion air that is heated and supplied to a furnace or steam generator. Hereinafter, the recovery gas stream shall be referred to as combustion air or air. In other forms of rotary regenerative heat exchangers, the sheets are stationary and the flue gas and the recovery gas ducts are rotated.